lm49370rl National Semiconductor Corporation, lm49370rl Datasheet - Page 37

• Manufacturer Part Number: lm49370rl
• Description: Audio Sub-system With An Ultra Low Emi, Spread Spectrum, Class D Loudspeaker Amplifier, A Dual-mode Stereo Headphone Amplifier, And A Dedicated Pcm Interface For Bluetooth Transceivers
• Manufacturer: National Semiconductor Corporation

Bits
2:1
5:4
12.17 MIC_2 CONFIGURATION REGISTER
This register is used to control the microphone configuration.
In OCL mode there is a trade-off between the external microphone supply voltage (EXT_MIC_BIAS - OCL_VCM_ VOLTAGE) and
the maximum output power possible from the headphones. A lower OCL_VCM_VOLTAGE gives a higher microphone supply
voltage but a lower maximum output power from the headphone amplifiers due to the lower OCL_VCM_VOLTAGE - A_V
0
3
2.9V to 3.4V
2.8V to 2.9V
2.7V to 2.8V
Available
A_V
> 3.4V
BUTTON_TYPE
DEBOUNCE_
DD
VOLTAGE
VOLTAGE
BUTTON_
BIAS_
VCM_
OCL_
MIC_
TIME
Field
EXT_MIC_BIAS
Recommended
This selects the voltage used as virtual ground (HP_VMID pin) in OCL mode. This will depend on the
available supply and the power output requirements of the headphone amplifiers.
This selects the voltage as a reference to the internal and external microphones. Only one bias pin is driven
at once depending on the INT_EXT bit setting found in the MIC_1 (0x0Bh) register. MIC_BIAS_VOLTAGE
should be set to '11' only if A_V
should not be used to generate the EXT_BIAS supply for a cellular headset external microphone. Please
refer to Table 19 for more detail.
If set, the LM49370 assumes that the button (if used) in the headset is in series (series push button) with
the microphone, opening the circuit when pressed. The default is for the button to be in parallel (parallel
push button), shorting out the microphone when pressed.
This sets the time used for debouncing the pushing of the button on a headset with a parallel push button.
3.3V
2.8V
2.5V
2.5V
OCL_VCM_VOLTAGE
MIC_BIAS_VOLTAGE
TABLE 19. External MIC Supply Voltages in OCL Mode
00
01
10
11
0
1
2
2
2
2
BUTTON_DEBOUNCE_TIME
TABLE 18. MIC_2 (0x0Ch)
OCL_VCM_VOLT = 1.5V
DD
00
01
10
11
> 3.4V. In OCL mode, MIC_BIAS_VOLTAGE = '00' (EXT_BIAS = 2.0V)
2
2
2
2
37
1.8V
1.3V
1.0V
-
Description
Supply to Microphone
EXT_BIAS/INT_BIAS
Voltage
1.2V
1.5V
2.0V
2.5V
2.8V
3.3V
OCL_VCM_VOLT = 1.2V
2.1V
1.6V
1.3V
1.3V
Time (ms)
16
32
0
8
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